This invention relates to motor graders in which a circle-mounted working implement, such as a blade or the like, is supported by means of guide shoes on a drawbar structure attached to the main frame of the motor grader and more particularly to such a motor grader including improved guide shoes which reduce the undesirable effects due to wearing of mating surfaces of the circle and drawbar structure in operation.
It will be understood that during grading operations it is often necessary to adjust the angle of the blade or other working implement of a motor grader with respect to the direction of travel of the motor grader. In the case of a blade such adjustment will depend upon the width of the strip of surface to be graded and upon the amount of material picked up by the blade at a particular point in the grading operation. Thus, the operator of the motor grader may make adjustments in the angle of the blade with respect to the direction of travel of the motor grader by rotating the circle upon which the blade is mounted about its axis. Structures of the prior art, usually including guide shoes, by which the circle-mounted working implement was supported on the drawbar of the motor grader, have seriously reduced the accuracy and smoothness of the graded surface which could be produced due to the working clearances and tolerances required in such supporting structure as well as the normally expected wear on the mating surfaces of the supporting structure.
It will be understood that the vertical positioning of a blade with respect to the surface to be graded is established by one control means of the motor grader and that any change in such vertical positioning due to the operation of further control means for adjusting the angle of the blade with respect to the direction of travel of the motor grader will reduce the smoothness and accuracy of the resulting grade surface. Modern motor graders use an automatic blade control (A. B. C.) device for reading the desired grade level from a reference grade line or wire and automatically adjusting the vertical positioning of the blade to maintain the reference level. However, such devices cannot compensate for changes in the vertical positioning of the blade which will result from any lost motion present in the supporting structure for the blade. In motor graders of the prior art, an attempt was made to hold working clearances and tolerances to a minimum, however, such working clearances and tolerances were subject to radical change in operation due to wearing of mating surfaces of such structures. Since tolerances as small as 1/8 inch are now required in road grading operations, it will be seen that any appreciable lost motion in the supporting structure due to wear and working tolerances will increase the difficulty of maintaining the required grade tolerance.